Highly refractive glass

ABSTRACT

A glass includes the following components in % by weight: 2-10 wt-% SiO2, 2-10 wt-% B2O3, 40-55 wt-% La2O3, 4-11 wt-% Gd2O3, 6-14 wt-% Nb2O5, 8-18.5 wt-% TiO2, and 5-11 wt-% ZrO2. The glass has a refractive index nd of at least 2.02, a sum of the portions of La2O3, Nb2O5, TiO2 and ZrO2 is at least 76.5% by weight, and a weight ratio of a sum of the portions of La2O3, Nb2O5 and ZrO2 to the portion of TiO2 is at least 3.85:1.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to German Patent Application No. DE 102020 120 171.0 filed on Jul. 30, 2020, which is incorporated in itsentirety herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to glasses with high refractive index, inparticular a refractive index of higher than 2.00 in the whole visiblerange of the spectrum and/or a refractive index n_(d) of at least 2.02.The glasses may have a high transmittance in the visible wavelengthrange, in particular also in the lower visible wavelength range. Theinvention also relates to a method for the production of the glasses aswell as the use of the glasses. The glasses provided according to thepresent invention can in particular be used for AR eyeglasses. Furtheruses are, for example, uses as lens or wave guide in the optical field.

2. Description of the Related Art

The field of the so-called augmented reality (AR) has becomeincreasingly important. This is understood as the widening of reality,in particular by visually presented computer-generated information. Forthis purpose, often particular eyeglasses, so-called AR eyeglasses, areused. For the production of such eyeglasses, glasses with particularlyhigh refractive index are required, because they increase the field ofview (FoV). In addition, preferably, the glasses should have aparticularly good transmittance in the visible wavelength range. In thisconnection, in the case of particularly highly refractive glasses, inparticular the transmittance in the lower visible wavelength range, forexample in the blue range of 420 nm to 490 nm, inter alia at 420 nm or460 nm, has shown to be problematic. In this connection, this phenomenonis also described by the term “UV edge” of the glass. When the UV edgeis shifted too far into the visible range or does not rise steeplyenough, then the transmittance properties in the lower visiblewavelength range are not good. In addition, it has been shown to bedifficult to provide glasses with a particularly high refractive indexin the whole visible range (in particular from 380 nm to 750 nm). So,for example, glasses which have a refractive index n_(d) of 2.001, butat other wavelengths in the visible range do not achieve a refractiveindex of at least 2.000 are known.

In the past, in particular, glasses made of the niobium phosphate systemhave been used. However, in the production, these glasses are veryproblematic, because loss of oxygen, especially due to high melting andrefining temperatures, in the already reducing phosphate system resultsin lower oxidation states of Nb than V and thus in an intensive brown upto even black coloration. Furthermore, this glass family does not onlytend to interfacial crystallization, like the lanthanum borates orborosilicate systems, but also exhibits a very fast crystal growth,which makes aftercooling (stress cooling or refractive power adjustment)critical for optionally pre-nucleated glasses. In addition, the glass isrelatively brittle and therefore it is difficult to polish it into thinwafers.

What is needed in the art is glasses having a refractive index of higherthan 2.0 in the whole visible range of the spectrum and/or a refractiveindex n_(d) of at least 2.02. The glasses may be characterized byexcellent transmittance properties, in particular also in the lowervisible wavelength range, for example at 420 nm and/or 460 nm. Inaddition, the batch costs shall remain moderate. The glass should becharacterized by a good potential for being manufactured withoutstreaks. In addition, it should be possible to produce wafers out of theglass in good yield. In particular, good hot glass forming and goodprocessing of the glass should be possible. The glasses should have adensity which is as low as possible, despite the high refractive index.So, in particular, the wearing comfort of the AR eyeglasses can beincreased.

SUMMARY OF THE INVENTION

In some exemplary embodiments provided according to the presentinvention, a glass includes the following components in % by weight:2-10 wt-% SiO₂, 2-10 wt-% B₂O₃, 40-55 wt-% La₂O₃, 4-11 wt-% Gd₂O₃, 6-14wt-% Nb₂O₅, 8-18.5 wt-% TiO₂, and 5-11 wt-% ZrO₂. The glass has arefractive index n_(d) of at least 2.02, a sum of the portions of La₂O₃,Nb₂O₅, TiO₂ and ZrO₂ is at least 76.5% by weight, and a weight ratio ofa sum of the portions of La₂O₃, Nb₂O₅ and ZrO₂ to the portion of TiO₂ isat least 3.85:1.

In some exemplary embodiments provided according to the presentinvention, a glass has a refractive index n_(d) of at least 2.02 and aninternal transmission TI of at least 85%, measured at a wavelength of460 nm and a sample thickness of 10 mm.

In some exemplary embodiments provided according to the presentinvention, a glass article includes a glass having a refractive indexn_(d) of at least 2.02 and being in the form of at least one of: a glassfor eyeglasses; a stack of wafers; a wafer; a wafer with a maximumdiameter of 5.0 cm to 40.0 cm; a lens; a spherical lens; a prism; anasphere; a light wave guide; a fiber; or a plate. The glass has aninternal transmission TI of at least 85%, measured at a wavelength of460 nm and a sample thickness of 10 mm.

DETAILED DESCRIPTION OF THE INVENTION

In some exemplary embodiments provided according to the presentinvention, a glass is provided that comprises the following componentsin % by weight:

Component Portion (% by weight) SiO₂ 2-10 B2O₃ 2-10 La₂O₃ 40-55  Gd₂O₃4-11 Nb₂O₅ 6-14 TiO₂  8-18.5 ZrO₂ 5-11the glass having a refractive index n_(d) of at least 2.02. The sum ofthe portions of La₂O₃, Nb₂O₅, TiO₂ and ZrO₂ is at least 76.5% by weight,and the weight ratio of the sum of the portions of La₂O₃, Nb₂O₅ and ZrO₂to the portion of TiO₂ is at least 3.85:1.

In some exemplary embodiments provided according to the presentinvention, a glass is provided that comprises the following componentsin % by weight:

Component Portion (% by weight) SiO₂ 2-10 B₂O₃ 2-10 La₂O₃ 40-55  Gd₂O₃4-11 Nb₂O₅ 6-14 TiO₂  8-18.5 ZrO₂ 5-11the glass having a refractive index n_(d) of at least 2.03. The sum ofthe portions of La₂O₃, Nb₂O₅, TiO₂ and ZrO₂ is at least 76.5% by weight,the weight ratio of the sum of the portions of La₂O₃, Nb₂O₅ and ZrO₂ tothe portion of TiO₂ is at least 3.85:1, and the internal transmission TIof the glass, measured at a wavelength of 460 nm and a sample thicknessof 10 mm, is at least 84% or at least 85%.

In some embodiments, the glass comprises the following components in %by weight:

Component Portion (% by weight) SiO₂ 4-9 B₂O₃ 4-8 La₂O₃ 44-50 Gd₂O₃4.5-9  Nb₂O₅  8-12 TiO₂  9-17 ZrO₂ 6-8

In some embodiments, the glass comprises the following components in %by weight:

Component Portion (% by weight) SiO₂ 2-10 B₂O₃ 2-10 La₂O₃ 40-55  Gd₂O₃4.5-9   Nb₂O₅ 6-14 TiO₂  8-18.5 ZrO₂ 6-11

In some embodiments, the glass comprises the following components in %by weight:

Component Portion (% by weight) SiO₂ 2-10 B₂O₃ 2-10 La₂O₃ 40-55  Gd₂O₃4-9  Nb₂O₅ 6-14 TiO₂  8-18.5 ZrO₂ 6-11

In some embodiments, the glass comprises the following components in %by weight:

Component Portion (% by weight) SiO₂ 2-10 B₂O₃ 2-10 La₂O₃ 40-55  Gd₂O₃4-11 Nb₂O₅ 6-14 TiO₂  8-18.5 ZrO₂ 5-11 BaO 1-8 

In some embodiments, the glass comprises the following components in %by weight:

Component Portion (% by weight) SiO₂ 2-10 B₂O₃ 2-10 La₂O₃ 40-55  Gd₂O₃4-11 Nb₂O₅ 6-14 TiO₂  8-18.5 ZrO₂ 5-11 BaO 2-6 

In some embodiments, the glass comprises the following components in %by weight:

Component Portion (% by weight) SiO₂ 2-10 B₂O₃ 2-10 La₂O₃ 40-55  Gd₂O₃4-11 Nb₂O₅ 6-14 TiO₂  8-18.5 ZrO₂ 5-11 BaO 3-5 

In some exemplary embodiments provided according to the presentinvention, a glass is provided with a refractive index n_(d) in a rangeof 2.02 to 2.08, such as of 2.03 to 2.07 or of 2.04 to 2.06 and aninternal transmission TI of at least 85%, such as at least 90%, at least91%, at least 92%, at least 93%, at least 94%, at least 95%, at least96%, or at least 97%, the internal transmission being measured at awavelength of 460 nm and a sample thickness of 10 mm.

In some exemplary embodiments provided according to the presentinvention, a glass is provided with a refractive index n_(d) of at least2.02, at least 2.03, or at least 2.04, and an internal transmission TIof at least 85%, such as at least 90%, at least 91%, at least 92%, atleast 93%, at least 94%, at least 95%, at least 96%, or at least 97%,the internal transmission being measured at a wavelength of 460 nm and asample thickness of 10 mm.

The internal transmission and the internal transmission factor,respectively, can be measured with methods which are known by a personskilled in the art, for example, according to DIN 5036-1:1978. In thisdescription, the data given in connection with the internal transmissionrelate to a sample thickness of 10 mm. The mention of a “samplethickness” does not mean that the glass has this thickness, but it doesonly mean that the data given in connection with the internaltransmission relate to this thickness.

Unless otherwise stated or obvious for a person skilled in the art, heredescribed measurements are conducted at 20° C. and 101.3 kPa airpressure.

The glass provided according to the invention has a refractive indexn_(d) of at least 2.02. In some embodiments, the refractive index n_(d)is in a range of 2.02 to 2.08, such as of 2.03 to 2.07 or of 2.04 to2.06. The refractive index n_(d) is known to a person skilled in theart, and it is, in particular, the refractive index at a wavelength ofabout 587.6 nm (wavelength of the d line of helium). A person skilled inthe art knows how the refractive index n_(d) can be determined. Theglass provided according to the invention may, for example, have arefractive index n_(d) of at least 2.02, at least 2.03, or at least2.04. The glass provided according to the invention may, for example,have a refractive index n_(d) of at most 2.08, at most 2.07, or at most2.06.

In some embodiments, the refractive index is determined with the help ofa refractometer, in particular with the help of a V block refractometer.Here, in particular, samples having a square or nearly square base(e.g., with dimensions of about 20 mm×20 mm×5 mm) can be used. When ameasurement with a V block refractometer is conducted, then the samplesnormally are placed in a V-shaped block prism with known refractiveindex. The refraction of an incident light beam depends on thedifference between the refractive index of the sample and the refractiveindex of the V block prism so that it is possible to determine therefractive index of the sample. The measurement may be conducted at atemperature of 22° C.

The refractive index depends on the wavelength of the light and can bedetermined at different wavelengths, for example n_(d) at about 587.6nm, nF at about 486 nm and nC at about 656 nm. In some embodiments, theglass has in the whole visible range of the spectrum (in particular of380 nm to 750 nm) a refractive index of higher than 2.00, such as ofhigher than 2.01. In some embodiments, the refractive index of the glassin the whole visible range of the spectrum is in a range of 2.00 to2.10, for example of 2.01 to 2.09, of 2.02 to 2.08, of 2.03 to 2.07, orof 2.04 to 2.06. The refractive index of the glass in the whole visiblerange of the spectrum may, for example, be at least 2.00, at least 2.01,at least 2.02, at least 2.03, or at least 2.04. The refractive index ofthe glass in the whole visible range of the spectrum may, for example,be at most 2.10, at most 2.09, at most 2.08, at most 2.07, or at most2.06.

The refractive index nF is the refractive index at a wavelength of about486 nm. The refractive index nF of the glasses provided according to thepresent invention may be in a range of 2.00 to 2.10, for example of 2.01to 2.09, of 2.02 to 2.08, of 2.03 to 2.07, or of 2.04 to 2.06. Therefractive index nF may, for example, be at least 2.00, at least 2.01,at least 2.02, at least 2.03 or at least 2.04. The refractive index nFmay, for example, be at most 2.10, at most 2.09, at most 2.08, at most2.07, or at most 2.06.

The refractive index nC is the refractive index at a wavelength of about656 nm. The refractive index nC of the glasses provided according to thepresent invention may be in a range of 2.00 to 2.06, for example of 2.01to 2.05, or of 2.02 to 2.04. The refractive index nC may, for example,be at least 2.00, at least 2.01, or at least 2.02. The refractive indexnC may, for example, be at most 2.06, at most 2.05, or at most 2.04.

In some embodiments, the glass has a dispersion v_(d) of 20.0 to 35.0,for example of 22.5 to 32.5 or of 25.0 to 30.0. The dispersion v_(d)may, for example, be at least 20.0, at least 22.5, or at least 25.0. Thedispersion v_(d) may, for example, be at most 35.0, at most 32.5, or atmost 30.0.

The density of the glasses provided according to the present inventionmay be in a range of 4.90 g/cm³ to 5.50 g/cm³, such as of 4.95 g/cm³ to5.40 g/cm³, or of 5.00 g/cm³ to 5.35 g/cm³. The density may, forexample, be at least 4.90 g/cm³, at least 4.95 g/cm³, or at least 5.00g/cm³. The density may, for example, be at most 5.50 g/cm³, at most 5.40g/cm³, or at most 5.35 g/cm³. In some embodiments, the density of theglasses is lower than 5.30 g/cm³, such as lower than 5.25 g/cm³, lowerthan 5.20 g/cm³, or lower than 5.15 g/cm³.

It is known that the density of glasses increases with increasingrefractive index. In some embodiments, however, the glasses providedaccording to the present invention are in particular also characterizedby the fact that the density, despite the high refractive index, isrelatively low. The ratio of density to the refractive index n_(d) maybe in a range of 2.30 to 2.80 g/cm³, such as of 2.35 to 2.75 g/cm³, of2.40 to 2.70 g/cm³, of 2.45 to 2.65 g/cm³, or of 2.50 to 2.60 g/cm³. Theratio of density and refractive index n_(d) is determined by dividingthe value of the density (in g/cm³) by the value of the refractive indexn_(d). In some embodiments, the ratio of density to the refractive indexn_(d) is lower than 2.80 g/cm³, such as lower than 2.75 g/cm³, lowerthan 2.70 g/cm³, lower than 2.65 g/cm³, lower than 2.60 g/cm³, or lowerthan 2.55 g/cm³.

In some embodiments, the glass provided according to the presentinvention has a high transmittance in the visible range, in particularalso in the lower visible wavelength range, for example at 420 nm and/or460 nm. Thus, in some embodiments, the UV edge can be found atrelatively low wavelengths, despite the highly refractive properties.

In some embodiments, the internal transmission TI of the glass, measuredat a wavelength of 420 nm and a sample thickness of 10 mm, is at least25%, such as at least 30%, at least 40%, at least 50%, at least 60%, atleast 70%, at least 75%, at least 80%, at least 85%, at least 87.5%, orat least 90%. In some embodiments, the internal transmission TI of theglass, measured at a wavelength of 420 nm and a sample thickness of 10mm, is at most 99%, at most 98%, at most 95%, or at most 92.5%.

In some embodiments, the internal transmission TI of the glass, measuredat a wavelength of 460 nm and a sample thickness of 10 mm, is at least63%, such as at least 65%, at least 70%, at least 75%, at least 80%, atleast 85%, at least 87.5%, at least 90%, at least 91%, at least 92%, atleast 93%, at least 94%, at least 95%, at least 96%, or at least 97%. Insome embodiments, the internal transmission TI of the glass, measured ata wavelength of 460 nm and a sample thickness of 10 mm, is at most99.99%, at most 99.9%, at most 99%, or at most 98%.

When T_(g) is very high, then the aftercooling lasts longer. However,T_(g) is also a measure for the chemical stability and hardness (thehigher T_(g), the more stable the network and thus harder and chemicallymore resistant the glass). While a high chemical resistance is good, ahardness which is too high is also expensive again, because the grindingand polishing last longer and have to be conducted with highercarefulness, so that during it not too many microcracks are generated.Therefore, in some embodiments, the glass transition temperature T_(g)of the glass provided according to the present invention is in a rangeof 700° C. to 800° C., such as of 710° C. to 780° C., of 720° C. to 760°C., or of 730° C. to 750° C. The glass transition temperature T_(g) may,for example, be at least 700° C., at least 710° C., at least 720° C., orat least 730° C. The glass transition temperature T_(g) may, forexample, be at most 800° C., at most 780° C., at most 760° C., or atmost 750° C.

The temperature T1 at which the viscosity is 10¹ dPas may be in a rangeof 1100° C. to 1250° C., such as in a range of 1150° C. to 1200° C.Thus, the glass composition provided according to the present inventionallows particularly low meltdown temperatures. The temperature T1 may,for example, be at least 1100° C. or at least 1150° C. The temperatureT1 may, for example, be at most 1250° C. or at most 1200° C.

The temperature T4 at which the viscosity is 10⁴ dPas may be in a rangeof 875° C. to 1025° C., such as in a range of 925° C. to 975° C. Thetemperature T4 may, for example, be at least 875° C. or at least 925° C.The temperature T4 may, for example, be at most 1025° C. or at most 975°C.

The softening temperature T7.6 at which the viscosity is 10^(7.6) dPasmay be in a range of 750° C. to 900° C., of 800° C. to 850° C. Thesoftening temperature T7.6 may, for example, be at least 750° C. or atleast 800° C. The softening temperature T7.6 may, for example, be atmost 900° C. or at most 850° C.

The crystallization temperature TK may be in a range of 1000° C. to1200° C., such as of 1025° C. to 1175° C. or of 1050° C. to 1150° C. Theviscosity at TK may be in a range of 10 to 100 dPas. The crystallizationtemperature TK may, for example, be at least 1000° C., at least 1025°C., or at least 1050° C. The crystallization temperature TK may, forexample, be at most 1200° C., at most 1175° C., or at most 1150° C.

The viscosity of a glass can be determined with the help of a rotationalviscometer, e.g., according to DIN ISO 7884-2:1998-2. The dependence ofthe viscosity on the temperature can be determined by using the VFTcurve (Vogel-Fulcher-Tammann equation). The softening temperature can bedetermined with the help of the fiber elongation viscometer according toISO 7884-2.

In some embodiments, the glasses provided according to the inventionhave a coefficient of thermal expansion (CTE) in the temperature rangeof 20° C. to 300° C. (CTE(20,300)) which is in a range of 6.7 to 10.0ppm/K, such as of 7.0 to 9.7 ppm/K, of 7.3 to 9.4 ppm/K, of 7.6 to 9.1ppm/K, of 7.9 to 8.8 ppm/K, of 8.0 to 8.7 ppm/K, or of 8.1 to 8.6 ppm/K.The CTE should be well in line with coatings, wherein in particular veryhigh CTE values often result in problems, because in this range thepolymer often is not characterized by a linear CTE profile, but by asteeper one. When then the glass, in addition, has an unsuitable CTE,then it may be that cracks are formed or layers are peeled off. Forthese reasons, inter alia, the above-mentioned CTE values may beadvantageous. The CTE may, for example, be at least 6.7 ppm/K, at least7.0 ppm/K, at least 7.3 ppm/K, at least 7.6 ppm/K, at least 7.9 ppm/K,at least 8.0 ppm/K, or at least 8.1 ppm/K. The CTE may, for example, beat most 10.0 ppm/K, at most 9.7 ppm/K, at most 9.4 ppm/K, at most 9.1ppm/K, at most 8.8 ppm/K, at most 8.7 ppm/K, or at most 8.6 ppm/K.

The glass provided according to the present invention contains SiO₂ in aportion of 2 to 10% by weight, such as 4 to 9% by weight. SiO₂ is aglass former. The oxide very strongly improves the chemical resistance,but also increases the processing temperatures. When it is used in veryhigh amounts, then the refractive indices according to the presentinvention cannot be achieved. In some embodiments, the portion of SiO₂is in a range of 4.5 to 7% by weight, of 4.75 to 6.5% by weight, or of 5to 6% by weight. The portion of SiO₂ may, for example, be at least 2% byweight, at least 4% by weight, at least 4.5% by weight, at least 4.75%by weight, or at least 5% by weight. The portion of SiO₂ may, forexample, be at most 10% by weight, at most 9% by weight, at most 7% byweight, at most 6.5% by weight, or at most 6% by weight.

B₂O₃ has been shown to be particularly suitable for achieving lowmeltdown temperatures. But, in particular due to its corrosiveness withrespect to melting tank materials, the content of B₂O₃ is limited. Theglass provided according to the present invention contains B₂O₃ in aportion of 2 to 10% by weight, such as of 3 to 9% by weight, of 4 to8.5% by weight, 5 to 8% by weight, or 5.25 to 6.5% by weight. Theportion of B₂O₃ may, for example, be at least 2% by weight, at least 3%by weight, at least 4% by weight, at least 5% by weight, or at least5.25% by weight. The portion of B₂O₃ may, for example, be at most 10% byweight, at most 9% by weight, at most 8.5% by weight, at most 8% byweight, or at most 6.5% by weight.

When the sum of the weight portions of SiO₂ and B₂O₃ is very high, thenthis negatively influences the refractive index. On the other hand, SiO₂and B₂O₃ are required as network formers so that the portion should alsonot be very low. The sum of the weight portions of SiO₂ and B₂O₃ may be6 to 16% by weight, such as 7 to 15% by weight, 8 to 14% by weight, or 9to 13% by weight. The sum of the weight portions of SiO₂ and B₂O₃ may,for example, be at least 6% by weight, at least 7% by weight, at least8% by weight, or at least 9% by weight. The sum of the weight portionsof SiO₂ and B₂O₃ may, for example, be at most 16% by weight, at most 15%by weight, at most 14% by weight, or at most 13% by weight.

In some embodiments, the weight portion of SiO₂ is higher than theweight portion of B₂O₃, because SiO₂ does not attack the refractorymaterial, in contrast to B₂O₃. But, B₂O₃ is more advantageous for themelting down behavior. Therefore, in some embodiments, SiO₂ and B₂O₃ arepresent in comparable portions. The weight ratio of the portion of SiO₂to the portion of B₂O₃ may be in a range of 0.45:1 to 1.45:1, of 0.55:1to 1.35:1, of 0.65:1 to 1.25:1. In some embodiments, the portion of B₂O₃is at least as high as the portion of SiO₂. The weight ratio of theportion of SiO₂ to the portion of B₂O₃ can advantageously be used forsuitably adjusting meltdown temperature and corrosiveness of the melt.The weight ratio of the portion of SiO₂ to the portion of B₂O₃ may, forexample, be at least 0.45:1, at least 0.55:1, or at least 0.65:1. Theweight ratio of the portion of SiO₂ to the portion of B₂O₃ may, forexample, be at most 1.45:1, at most 1.35:1, or at most 1.25:1. In someembodiments, the weight ratio of the portion of SiO₂ to the portion ofB₂O₃ is at least 1:1 or higher than 1:1, for example at least 1.01:1, atleast 1.02:1, at least 1.03:1, or at least 1.04:1.

The sum of the portions of La₂O₃, Nb₂O₅, TiO₂ and ZrO₂ in the glassprovided according to the present invention is at least 76.5% by weight.In some embodiments, the sum of the portions of La₂O₃, Nb₂O₅, TiO₂ andZrO₂ is in a range of 76.5% by weight to 85% by weight, such as of 77%by weight to 84% by weight, of 78% by weight to 83% by weight, or of 79%by weight to 82.5% by weight. In some embodiments, the sum of theportions of La₂O₃, Nb₂O₅, TiO₂ and ZrO₂ in the glass provided accordingto the present invention is even at least 80% by weight. A high portionof these components is advantageous for achieving a particularly highrefractive index. But it is also possible that the tendency tocrystallization increases so that it may be advantageous to limit thecontent. The sum of the portions of La₂O₃, Nb₂O₅, TiO₂ and ZrO₂ may, forexample, be at least 76.5% by weight, at least 77% by weight, at least78% by weight, or at least 79% by weight. The sum of the portions ofLa₂O₃, Nb₂O₅, TiO₂ and ZrO₂ may, for example, be at most 85% by weight,at most 84% by weight, at most 83% by weight, or at most 82.5% byweight.

The weight ratio of the sum of the portions of La₂O₃, Nb₂O₅, TiO₂ andZrO₂ to the sum of the portions of SiO₂ and B₂O₃ may be in a range of6.25:1 to 8.35:1, such as of 6.75:1 to 7.85:1, of 6.95:1 to 7.65:1, of7.05:1 to 7.55:1, or of 7.15:1 to 7.45:1. The weight ratio of the sum ofthe portions of La₂O₃, Nb₂O₅, TiO₂ and ZrO₂ to the sum of the portionsof SiO₂ and B₂O₃ may, for example, be at least 6.25:1, at least 6.75:1,at least 6.95:1, at least 7.05:1, or at least 7.15:1. The weight ratioof the sum of the portions of La₂O₃, Nb₂O₅, TiO₂ and ZrO₂ to the sum ofthe portions of SiO₂ and B₂O₃ may, for example, be at most 8.35:1, atmost 7.85:1, at most 7.65:1, at most 7.55:1, or at most 7.45:1.

La₂O₃ with a portion of 40 to 55% by weight is one of the maincomponents of the glass provided according to the present invention.La₂O₃, together with SiO₂ and B₂O₃, forms the dense glass network intowhich TiO₂ is inserted. La₂O₃ is stable and not redox sensitive as wellas also with respect to price and availability more favorable than Gd₂O₃and Nb₂O₅. In some embodiments, the portion of La₂O₃ is in a range of 44to 50% by weight, such as of 45 to 49% by weight. When the portion ofLa₂O₃ to the disadvantage of other highly refractive components isincreased, then this results in a negative influence onto the refractiveindex. In addition, in the case of very high portions of La₂O₃ also thetendency to crystallization increases. The portion of La₂O₃ may, forexample, be at least 40% by weight, at least 44% by weight, or at least45% by weight. The portion of La₂O₃ may, for example, be at most 55% byweight, at most 50% by weight, or at most 49% by weight.

In some embodiments, the glasses provided according to the presentinvention have a weight ratio of the sum of the portions of SiO₂ andB₂O₃ to the portion of La₂O₃ in a range of 0.10:1 to 0.40:1, such as of0.15:1 to 0.35:1, of 0.16:1 to 0.32:1, of 0.18:1 to 0.28:1, of 0.20:1 to0.26:1, or of 0.21:1 to 0.25:1. The weight ratio of the sum of theportions of SiO₂ and B₂O₃ to the portion of La₂O₃ may, for example, beat least 0.10:1, at least 0.15:1, at least 0.16:1, at least 0.18:1, atleast 0.20:1, or at least 0.21:1. The weight ratio of the sum of theportions of SiO₂ and B₂O₃ to the portion of La₂O₃ may, for example, beat most 0.40:1, at most 0.35:1, at most 0.32:1, at most 0.28:1, at most0.26:1, or at most 0.25:1.

In addition to its high influence onto the refractive index, Nb₂O₅ alsohas a positive influence onto the glass density. With this component thedensities can be reduced. But it can exhibit a tendency to loss ofoxygen and formation of lower oxidation states and thus to a moreintensive coloration. The glasses provided according to the presentinvention contain Nb₂O₅ in a portion of 6 to 14% by weight, such as 8 to12% by weigh or 10 to 12% by weight. The portion of Nb₂O₅ may, forexample, be at least 6% by weight, at least 8% by weight, or at least10% by weight. The portion of Nb₂O₅ may, for example, be at most 14% byweight, at most 13% by weight, or at most 12% by weight.

The sum of the portions of La₂O₃ and Nb₂O₅ may be in a range of 48 to67% by weight, such as of 50 to 65% by weight, of 52.5 to 62.5% byweight, or of 55 to 60% by weight. In some embodiments, the sum of theportions of La₂O₃ and Nb₂O₅ is at least 48% by weight, such as at least50% by weight, at least 52.5% by weight, at least 55% by weight, or atleast 57.5% by weight. The sum of the portions of La₂O₃ and Nb₂O₅ may,for example, be at most 67% by weight, at most 65% by weight, at most62.5% by weight, or at most 60% by weight.

The glasses provided according to the present invention contain TiO₂ ina portion of 8 to 18.5% by weight, such as 9 to 18% by weight, 12 to 17%by weight, or 14.5 to 16.5% by weight. TiO₂ makes a notable contributionto a high refractive index, and it also helps to maintain the densityrelatively low. But a limitation of the portion of TiO₂ is advantageous,because as nucleating agent it may make a contribution to crystal growthso that hot post-processing, for example pressing, is complicated. Insome embodiments, the portion of TiO₂ is at most 18.5% by weight, atmost 18% by weight, at most 17% by weight, or at most 16.5% by weight.The portion of TiO2 may, for example, be at least 8% by weight, at least9% by weight, at least 12% by weight, or at least 14.5% by weight.

In contrast to TiO₂, ZrO₂ does not exhibit any tendency to the formationof lower colored oxidation states. But, both, its solubility and alsothe velocity with which ZrO₂ is dissolved are limited. Higher portionsof ZrO₂ are unfavorable, because for complete dissolution highertemperatures are required which in turn has a negative influence ontothe transmittance. In addition, the purity of ZrO₂ is not very high (inparticular impurities with Fe). Therefore, at the upper end, the contentof ZrO₂ is limited. The portion of ZrO₂ in the glasses providedaccording to the preset invention is 5 to 11% by weight, such as 6 to 8%by weight or 6.25 to 7.5% by weight. A limitation of the portion of ZrO₂is also advantageous for confining potential crystal growth. In someembodiments, the portion of ZrO₂ is at least 5% by weight, at least 5.5%by weight, at least 6% by weight, at least 6.25% by weight, or at least6.5% by weight. The portion of ZrO₂ may, for example, be at most 11% byweight, at most 8% by weight, at most 7.5% by weight, at most 7% byweight, or at most 6.75% by weight.

TiO₂ and ZrO₂ make a notable contribution to a high refractive index,wherein in particular TiO₂ also makes a contribution to a relatively lowdensity. But, on the other hand, the portions of TiO₂ and ZrO₂ shouldalso not be too high, in particular in view of solubility, nucleationand crystallization. The sum of the portions of TiO₂ and ZrO₂ may be ina range of 15 to 30% by weight, such as of 17.5 to 27.5% by weight or of20 to 25% by weight. In some embodiments, the sum of the portions ofTiO₂ and ZrO₂ is at least 15% by weight, such as at least 17.5% byweight, at least 20% by weight, at least 21% by weight, at least 22% byweight, or even at least 22.7% by weight. The sum of the portions ofTiO₂ and ZrO₂ may, for example, be at most 30% by weight, at most 27.5%by weight, or at most 25% by weight.

The possible portion of TiO₂ in the glass is limited due to the tendencyto crystallization. In addition, TiO₂ also absorbs in the bluewavelength range, even as Ti(IV), while Nb(V) absorbs in the UV. But,reduced Nb₂O₅ causes considerably more absorption in the visible rangethan reduced TiO₂. In contrast thereto, La₂O₃ is stable and not redoxsensitive. According to this, it is advantageous, on the one hand, tolimit the portion of TiO₂ at the upper end, so that the UV absorption ofthe glass in the case of completely oxidized components is not shiftedtoo far into the visible range, but, on the other hand, to use the highn_(d) contribution and the low density contribution of TiO₂. La₂O₃ andNb₂O₅ also make a contribution to a high refractive index, theystabilize the network and maintain—as long as they remain oxidized—theUV transmittance in a higher range. According to this, it has been shownto be advantageous to adjust the weight ratio of the sum of the portionsof ZrO₂, La₂O₃ and Nb₂O₅ to the portion of TiO₂ in a targeted manner, inparticular to limit it at the lower end. The glasses provided accordingto the present invention have a weight ratio of the sum of the portionsof La₂O₃, Nb₂O₅ and ZrO₂ to the portion of TiO₂ of at least 3.85:1. Insome embodiments, the weight ratio of the sum of the portions of La₂O₃,Nb₂O₅ and ZrO₂ to the portion of TiO₂ is in a range of 3.85:1 to 5.25:1,such as of 3.90:1 to 5.00:1, of 3.95:1 to 4.75:1, for example 3.96:1 to4.50:1, 3.97:1 to 4.40:1, 3.98:1 to 4.35:1 or 3.99:1 to 4.30:1. In someembodiments, the weight ratio of the sum of the portions of La₂O₃, Nb₂O₅and ZrO₂ to the portion of TiO₂ is at least 3.85:1, at least 3.90:1, atleast 3.95:1, at least 3.96:1, at least 3.97:1, at least 3.98:1, atleast 3.99:1, or at least 4.00:1. The weight ratio of the sum of theportions of La₂O₃, Nb₂O₅ and ZrO₂ to the portion of TiO₂ may, forexample, be at most 5.25:1, at most 5.00:1, at most 4.75:1, at most4.50:1, at most 4.40:1, at most 4.35:1, at most 4.30:1, at most 4.25:1,at most 4.20:1, or at most 4.15:1.

In some embodiments, the weight ratio of the sum of the portions ofLa₂O₃ and Nb₂O₅ to the portion of TiO₂ is at least 3.15:1, such as atleast 3.25:1, at least 3.35:1, at least 3.46:1, at least 3.50:1, atleast 3.56:1, or at least 3.60:1. In some embodiments, the weight ratioof the sum of the portions of La₂O₃ and Nb₂O₅ to the portion of TiO₂ isin a range of 3.15:1 to 4.25:1, such as of 3.25:1 to 4.15:1, of 3.35:1to 4.05:1, of 3.46:1 to 3.94:1, of 3.50:1 to 3.90:1, of 3.56:1 to3.84:1, or of 3.60:1 to 3.80:1. The weight ratio of the sum of theportions of La₂O₃ and Nb₂O₅ to the portion of TiO₂ may, for example, beat most 4.25:1, at most 4.15:1, at most 4.05:1, at most 3.94:1, at most3.90:1, at most 3.84:1, or at most 3.80:1.

From the previously described considerations with respect to color,n_(d) contribution, density contribution and crystallization, it followsthat it is also advantageous to adjust the ratio of the portions of TiO₂and Nb₂O₅ in a targeted manner. So, it is possible, in particular, tochoose the composition so stable that only via increasing/decreasing ofSiO₂ the range of the refractive power can variably be adjusted. Theweight ratio of the portion of TiO₂ to the portion of Nb₂O₅ may be in arange of 1.05:1 to 1.75:1, such as of 1.15:1 to 1.65:1, or of 1.25:1 to1.55:1. The weight ratio of the portion of TiO₂ to the portion of Nb₂O₅may, for example, be at least 1.05:1, at least 1.15:1, or at least1.25:1. The weight ratio of the portion of TiO₂ to the portion of Nb₂O₅may, for example, be at most 1.75:1, at most 1.65:1, or at most 1.55:1.

In some embodiments, the weight ratio of the sum of the portions ofLa₂O₃ and Nb₂O₅ to the sum of the portions of TiO₂ and ZrO₂ is in arange of 2.15:1 to 3.05:1, such as of 2.25:1 to 2.95:1, of 2.35:1 to2.85, of 2.45:1 to 2.75:1, or of 2.55:1 to 2.65:1. In some embodiments,the weight ratio of the sum of the portions of La₂O₃ and Nb₂O₅ to thesum of the portions of TiO₂ and ZrO₂ is at least 2.15:1, such as atleast 2.25:1, at least 2.35:1, at least 2.45:1, at least 2.53:1, or atleast 2.55:1. The weight ratio of the sum of the portions of La₂O₃ andNb₂O₅ to the sum of the portions of TiO₂ and ZrO₂ may, for example, beat most 3.05:1, at most 2.95:1, at most 2.85:1, at most 2.75:1, or atmost 2.65:1.

The sum of the portions of Nb₂O₅ and ZrO₂ may be in a range of 12 to 24%by weight, of 14 to 22% by weight, or of 16 to 20% by weight. Inparticular, it is advantageous to limit the sum of the portions of Nb₂O₅and ZrO₂ at the upper end, because higher portions of ZrO₂ which is acomponent which is particularly difficult to solve may be particularlyproblematic in connection with high portions of Nb₂O₅. Because Nb₂O₅ inparticular crystallizes on interfacial areas, such as, for example, ZrO₂crystal seeds. So, in the case of re-pressing, slumping or aftercoolingalso in the volume very large crystals may grow in an uncontrolledmanner, and it is even possible that the cast product cracks. There isalso the risk that during slumping and in the worst case also cooling athick crystalline layer is formed which can only be removed withoutcracks with very high difficulties. The sum of the portions of Nb₂O₅ andZrO₂ may, for example, be at least 12% by weight, at least 14% byweight, or at least 16% by weight. The sum of the portions of Nb₂O₅ andZrO₂ may, for example, be at most 24% by weight, at most 22% by weight,or at most 20% by weight.

Thus, the glass compositions provided according to the present inventionare based on a balance of most different, partially contrary effects.When the portions of non-coloring components are increased too strongly,then this may have a negative influence onto the stability of the glass.Also, in some embodiments, the portions of TiO₂ and Nb₂O₅ are very high,wherein also here it is necessary to be careful due to crystallizationprocesses. TiO₂ is cheaper and has a more positive influence onto therefractive index, but with respect to the UV absorption it isdisadvantageous. Therefore, this results in the following described sumsand ratios which lead to advantageous glasses.

The weight ratio of the sum of the portions of TiO₂ and ZrO₂ to the sumof the portions of Nb₂O₅ and ZrO₂ may be in a range of 1.05:1 to 1.45:1,such as 1.10:1 to 1.40:1, 1.15:1 to 1.35:1, or 1.20:1 to 1.30:1. Theweight ratio of the sum of the portions of TiO₂ and ZrO₂ to the sum ofthe portions of Nb₂O₅ and ZrO₂ may, for example, be at least 1.05:1, atleast 1.10:1, at least 1.15:1, or at least 1.20:1. The weight ratio ofthe sum of the portions of TiO₂ and ZrO₂ to the sum of the portions ofNb₂O₅ and ZrO₂ may, for example, be at most 1.45:1, at most 1.40:1, atmost 1.35:1, or at most 1.30:1.

In some embodiments, the sum of the weight portions of Nb₂O₅ and ZrO₂ ishigher than the weight portion of TiO₂. In some embodiments, the weightratio of the sum of the portions of Nb₂O₅ and ZrO₂ to the portion ofTiO₂ is in a range of 1.05:1 to 1.25:1. In some embodiments, the weightratio of the sum of the portions of Nb₂O₅ and ZrO₂ to the portion ofTiO₂ is higher than 1.10:1, for example 1.11:1 to 1.20:1. The weightratio of the sum of the portions of Nb₂O₅ and ZrO₂ to the portion ofTiO₂ may, for example, be at least 1.05:1, higher than 1.10:1, or atleast 1.11:1. The weight ratio of the sum of the portions of Nb₂O₅ andZrO₂ to the portion of TiO₂ may, for example, be at most 1.25:1, or atmost 1.20:1.

The sum of the portions of La₂O₃, Nb₂O₅ and ZrO₂ may be in a range of 55to 75% by weight, such as of 57.5 to 72.5% by weight or of 60 to 70% byweight. In some embodiments, the sum of the portions of La₂O₃, Nb₂O₅ andZrO₂ is at least 55% by weight, at least 57.5% by weight, at least 60%by weight, or even at least 62.0% by weight or at least 64.0% by weight.The sum of the portions of La₂O₃, Nb₂O₅ and ZrO₂ may, for example, be atmost 75% by weight, at most 72.5% by weight, or at most 70% by weight.

In some embodiments, the weight ratio of the portion of TiO₂ to theportion of ZrO₂ is at most 3.00:1, such as at most 2.80:1, at most2.65:1, at most 2.60:1, at most 2.55:1, at most 2.50:1, at most 2.45:1,or at most 2.40:1. In some embodiments, the weight ratio of the portionof TiO₂ to the portion of ZrO₂ is in a range of 1.10:1 to 3.00:1, suchas of 1.30:1 to 2.80:1, of 1.50:1 to 2.65:1, of 1.70:1 to 2.60:1, of1.80:1 to 2.55:1, of 1.90:1 to 2.50:1, 2.00:1 to 2.45:1 or 2.10:1 to2.40:1. The weight ratio of the portion of TiO₂ to the portion of ZrO₂may, for example, be at least 1.10:1, at least 1.30:1, at least 1.50:1,at least 1.70:1, at least 1.80:1, or at least 1.90:1, at least 2.00:1,at least 2.10:1, at least 2.20:1, or at least 2.30:1.

The glasses provided according to the present invention contain Gd₂O₃ ina portion of 4 to 11% by weight, such as 4.5 to 9% by weight, 4.75 to8.5% by weight, or 5 to 8% by weight. Very high portions of Gd₂O₃ maynegatively influence the stability of the glass. The portion of Gd₂O₃may, for example, be at least 4% by weight, at least 4.5% by weight, atleast 4.75% by weight, or at least 5% by weight. The portion of Gd₂O₃may, for example, be at most 11% by weight, at most 10.5% by weight, atmost 10% by weight, at most 9.5% by weight, at most 9% by weight, atmost 8.5% by weight, at most 8% by weight, at most 7.5% by weight, atmost 7% by weight, at most 6.5% by weight, or at most 6% by weight.

The glasses provided according to the present invention may containY₂O₃. In some embodiments, the portion of Y₂O₃ is in a range of 0 to 5%by weight, for example 0.1 to 2% by weight, 0.2 to 1% by weight or 0.4to 0.8% by weight. Some embodiments are free of Y₂O₃. High portions ofY₂O₃ may have a negative influence onto the stability of the glass. Someembodiments contain at most 5% by weight, at most 2% by weight, at most1% by weight, at most 0.8% by weight, at most 0.7% by weight, at most0.6% by weight, at most 0.5% by weight, at most 0.2% by weight, or atmost 0.1% by weight Y₂O₃.

The glasses provided according to the present invention may contain BaO.On the one hand, BaO can stabilize high portions of TiO₂, however, onthe other hand, it may have a negative influence onto the refractiveindex. In some embodiments, the portion of BaO is in a range of 0 to 10%by weight, for example 1 to 8% by weight, 2 to 6% by weight or 3 to 5%by weight. Some embodiments are free of BaO. The portion of BaO may, forexample, be at least 0.5% by weight, at least 1% by weight, more than1.0% by weight, at least 1.1% by weight, at least 1.2% by weight, atleast 1.3% by weight, at least 1.4% by weight, at least 1.5% by weight,at least 1.6% by weight, at least 1.7% by weight, at least 1.8% byweight, at least 1.9% by weight, at least 2% by weight, at least 2.1% byweight, at least 2.2% by weight, at least 2.3% by weight, at least 2.4%by weight, at least 2.5% by weight, at least 2.6% by weight, at least2.7% by weight, at least 2.8% by weight, at least 2.9% by weight, or atleast 3% by weight. The portion of BaO may, for example, be at most 10%by weight, at most 8% by weight, at most 7% by weight, at most 6% byweight, or at most 5% by weight.

The weight ratio of the portion of TiO₂ to the portion of BaO may, forexample, be in a range of from 1.0:1 to 25:1, from 1.5:1 to 20:1, from2.0:1 to 15:1, from 2.5:1 to 10:1, from 3.0:1 to 7.5:1, from 3.5:1 to6.0:1, or from 4.0:1 to 5.0:1. The weight ratio of the portion of TiO₂to the portion of BaO may, for example, be at least 1.0:1, at least1.5:1, at least 2.0:1, at least 2.5:1, at least 3.0:1, at least 3.5:1,or at least 4.0:1. The weight ratio of the portion of TiO₂ to theportion of BaO may, for example, be at most 25:1, at most 20:1, at most15:1, at most 10:1, at most 7.5:1, at most 6.0:1, or at most 5.0:1.

The glasses provided according to the present invention may containHfO₂, in particular for increasing the refractive index. In someembodiments, the portion of HfO₂ is in a range of 0 to 1% by weight, forexample 0.1 to 0.5% by weight or 0.15 to 0.25% by weight. Low portionsof HfO₂ do normally not result in problems. Nevertheless, someembodiments are free of HfO₂. The portion of HfO₂ may, for example, beat most 1% by weight, at most 0.5% by weight, at most 0.25% by weight,at most 0.2% by weight, at most 0.15% by weight, or at most 0.1% byweight. The portion of HfO₂ may, for example, be at least 0.05% byweight, at least 0.10% by weight, or at least 0.15% by weight.

The glasses provided according to the present invention may containalkali metal oxides, in particular Li₂O. However, in some embodiments,the glass is free of alkali metal oxides. In some embodiments, theportion of Li₂O is in a range of 0 to 0.5% by weight, for example 0.05to 0.2% by weight. Li₂O is known for its corrosiveness with respect toceramic tank and crucible materials, and therefore, when possible, it isnot used or only used in low amounts. In some embodiments, the glass isfree of Li₂O. The portion of Li₂O may, for example, be at most 0.5% byweight, at most 0.2% by weight, or at most 0.1% by weight.

In one embodiment, the glass consists of at least 95.0% by weight, suchas of at least 98.0% by weight or of at least 99.0% by weight of thecomponents SiO₂, B₂O₃, La₂O₃, Gd₂O₃, Nb₂O₅, TiO₂ and ZrO₂, or of thecomponents SiO₂, B₂O₃, La₂O₃, Gd₂O₃, Nb₂O₅, TiO₂, ZrO₂ and BaO. In someembodiments, the glass substantially completely consists of thecomponents SiO₂, B₂O₃, La₂O₃, Gd₂O₃, Nb₂O₅, TiO₂, ZrO₂ and HfO₂, or ofthe components SiO₂, B₂O₃, La₂O₃, Gd₂O₃, Nb₂O₅, TiO₂, ZrO₂ and BaO.

In some embodiments, the glass provided according to the presentinvention is free of one or more constituents selected from MgO, CaO,SrO and ZnO. In some embodiments, the glass is free of MgO, CaO, SrO andZnO. These components decrease the refractive power and destabilize theglass. The same applies to Al₂O₃. Therefore, in some embodiments, theglass is free of Al₂O₃.

In some embodiments, the glass is free of one or more of theconstituents WO₃, Ta₂O₅ and/or GeO₂. In some embodiments, the glass isfree of WO₃, Ta₂O₅ and GeO₂. When these constituents are present, thenthe batch costs considerably increase.

The melts of the glass can be refined with the classical refiningagents. But, since the glasses can be melted in particular attemperatures of below 1300° C. and due to their low viscousness also arefining process at rather moderate temperatures is possible, for thebenefit of the UV transmittance, the content of, e.g., Sb₂O₃, As₂O₃and/or SnO₂ can be reduced (e.g., to <0.1% by weight), or they can beomitted (pure physical refining). Sb₂O₃, As₂O₃ and SnO₂ can be used asrefining agents. They are used only in low amounts. In particulararsenic and antimony are controversial due to health hazards. The glasscan be refined without chemical refining agents. Optionally, the glassmay comprise one or more of the following components having refiningeffect in the given portions in % by weight:

Sb₂O₃ 0.0 to 0.5 As₂O₃ 0.0 to 0.5 SnO₂ 0.0 to 0.5

The refining with SnO₂ requires comparatively high temperatures.Therefore, in some embodiments, SnO₂ is omitted. In some embodiments,the glasses provided according to the present invention are free ofSnO₂.

Sb₂O₃ has not proven to be very effective for refining, and theabsorption of Sb in the glass may deteriorate the UV edge. Therefore, insome embodiments, Sb₂O₃ is omitted. In some embodiments, the glassesprovided according to the present invention are free of Sb₂O₃.

In particular due to the health hazards, As₂O₃ can be omitted. In someembodiments, the glasses provided according to the present invention arefree of As₂O₃.

In some embodiments, sulfate can be used as refining agent. However,sulfate raw materials often involve iron which may entail adeterioration of the transmittance. Therefore, in some embodiments,sulfate raw materials are omitted. In some embodiments, the glassesprovided according to the present invention are free of sulfate.

In addition, neither As₂O₃ nor sulfate help against N₂ bubbles. When N₂bubbles occur, then, for avoiding them, it is possible to use, forexample, an atmosphere of protective gas, such as CO₂ or argon, forkeeping N₂ off the melt surface.

The glasses provided according to the present invention may be free ofabsorbing components, in particular free of components with absorptionin the visible range. In some embodiments, the glasses providedaccording to the present invention are free of Fe₂O₃.

In some embodiments, the glass is free of phosphate (P₂O₅), because in aconsiderable extent it makes the melt to a reducing one, and thus itconsiderably increases the oxygen demand of the melt.

In some embodiments, the glass is substantially free of one or more, forexample of all, constituents selected from lead, bismuth, cadmium,nickel, platinum, arsenic and antimony.

When in this description is mentioned that the glass is free of acomponent or that it does not contain a certain component, then thismeans that for this component at the most it is allowed to be present asan impurity in the glass. This means that it is not added in substantialamounts. According to the present invention, not substantial amounts areamounts of less than 200 ppm, such as less than 100 ppm, less than 50ppm or less than 10 ppm (m/m).

In some embodiments, the portion of platinum is exceptionally low,because platinum notably decreases the transmittance of the glass. Insome embodiments, the portion of platinum is lower than 5 ppm, such aslower than 3 ppm, lower than 1 ppm, lower than 50 ppb, or lower than 20ppb (m/m).

In some exemplary embodiments provided according to the presentinvention, a glass article comprises the described glass or consiststhereof. The glass article may have different forms. Optionally, thearticle has the form of

-   -   a glass for eyeglasses, such as a stack of wafers,    -   a wafer, in particular with a maximum diameter of 5.0 cm to 40.0        cm,    -   a lens, such as a spherical lens, a prism or an asphere, and/or    -   a light wave guide, such as a fiber or plate.

In some exemplary embodiments, the invention relates to the use of aglass or glass article described here in AR eyeglasses, wafer leveloptics, optical wafer applications, or the classical optics. In analternative or in addition, the glass described here or the glassarticle described here can be used as wafer, lens, spherical lens orlight wave guide.

In some exemplary embodiments provided according to the presentinvention, a method is provided for the production of a glass or glassarticle according to the present invention. The method comprises thefollowing steps:

-   -   melting of the glass raw materials,    -   optionally forming of a glass article from the glass melt,    -   cooling of the glass.

Due to the glass composition provided according to the presentinvention, the melting of the glass raw materials can be conducted atrelatively low meltdown temperatures. Relatively low meltdowntemperatures are advantageous, because with them the oxygen content ofthe batch is not reduced too strong, which otherwise may result in browncoloration by niobium or stronger yellow coloration by reduced titanium.In some embodiments, the melting of the glass raw materials is conductedat meltdown temperatures which are lower than 1400° C., such as lowerthan 1350° C. or lower than 1300° C.

The production method provided according to the present invention mayalso comprise a refining step. In some embodiments, also the refiningtemperatures are relatively low, such as lower than 1550° C., lower than1450° C., or lower than 1400° C. A purely physical refining process maybe used, thus without the addition of refining agents.

In some embodiments, bubbling of O₂ and passing over of O₂ are omitted.Due to the exemplary low process temperatures, also without addition ofO₂ the melt retains enough O₂ for maintaining the highest oxidationstates of, e.g., Nb(V) or Ti(IV) which are required for the UV edge,without additional Pt getting into the glass.

The cooling of the glass may be conducted with a cooling rate in a rangeof 1 K/h to 20 K/h, such as 1.15 K/h to 15 K/h or 1.3 K/h to 10 K/h. Lowcooling rates may be advantageous for reducing or avoiding stresses. Thecooling of the glass may, for example, be conducted with a cooling rateof at least 1 K/h, at least 1.15 K/h, or at least 1.3 K/h. The coolingof the glass may, for example, be conducted with a cooling rate of atmost 20 K/h, at most 15 K/h, or at most 10 K/h.

Examples

The example compositions shown in the following tables in % by weightwere melted, and their properties were examined. The cooling of theglass was conducted with a cooling rate of 10 K/h.

TABLE 1 1 2 3 4 5 6 7 8 9 SiO₂ 6.8 6.9 6.1 5.1 5.0 4.5 4.9 7.9 6.9 B₂O₃7.7 7.6 6.1 6.0 5.9 5.1 6.0 6.9 6.0 La₂O₃ 45.1 45.2 46.0 46.2 44.2 45.745.2 44.6 45.0 Gd₂O₃ 9.6 9.8 8.1 7.9 8.9 7.9 7.7 9.6 7.7 Nb₂O₅ 10.2 8.89.5 10.8 12.2 12.1 9.6 10.1 10.5 Y₂O₃ 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.60.6 TiO₂ 11.6 11.8 14.2 15.5 14.4 15.3 18.2 12.7 15.6 ZrO₂ 8.1 8.9 9.27.6 8.5 8.4 7.4 7.4 7.4 Sb₂O₃ 0.08 0.09 0.08 0.08 0.08 0.08 0.04 0.040.04 HfO₂ 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Σ (La₂O₃ + 75.0 74.7 78.880.1 79.3 81.6 80.5 74.8 78.6 Nb₂O₅ + TiO₂ + ZrO₂) Σ (La₂O₃ + 5.5 5.34.6 4.2 4.5 4.3 3.4 4.9 4.0 Nb₂O₅ + ZrO₂)/ TiO₂ Properties Density 5.115.12 5.18 5.21 5.23 5.30 5.17 5.08 5.11 [g/cm³] nd 1.9996 1.9975 2.03492.0550 2.0557 2.0760 2.0682 2.0023 2.0382 nF 1.9897 1.9877 2.0241 2.04362.0444 2.0660 2.0562 1.9922 2.0271 nC 1.9843 1.9823 2.0182 2.0374 2.03822.0497 1.9867 2.0210 νd 29.3 29.5 27.7 26.7 26.8 26.0 25.7 28.7 26.9 Tg[° C.] 730 730 743 743 738 754 747 735 741 TI(10 mm) 0.24 0.44 0.33 420nm TI(10 mm) 0.62 0.74 0.68 460 nm

TABLE 2 10 11 12 13 14 15 16 17 SiO₂ 6.9 6.7 4.0 6.0 6.5 4.1 5.1 6.9B₂O₃ 6.0 6.1 7.0 7.6 7.0 7.0 6.0 5.6 La₂O₃ 45.3 44.3 45.9 45.5 44.8 46.747.0 46.0 Gd₂O₃ 8.8 7.6 7.9 9.7 9.6 8.0 7.9 7.7 Nb₂O₅ 9.2 10.3 10.7 8.810.7 10.3 10.7 9.6 Y₂O₃ 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 TiO₂ 15.2 16.815.5 14.0 13.2 15.6 15.4 16.1 ZrO₂ 7.9 7.3 8.0 7.6 7.5 7.6 7.0 7.4 Li₂O0.1 Sb₂O₃ 0.04 0.04 HfO₂ 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Σ (La₂O₃ + 77.578.7 80.2 75.9 76.1 80.2 80.2 79.0 Nb₂O₅ + TiO₂ + ZrO₂) Σ (La₂O₃ + 4.13.7 4.2 4.4 4.8 4.1 4.2 3.9 Nb₂O₅ + ZrO₂)/ TiO₂ Properties Density 5.145.10 5.20 5.11 5.11 5.19 5.22 5.12 [g/cm³] nd 2.0323 2.0462 2.05472.0122 2.0151 2.0490 2.0537 2.0378 nF 2.0214 2.0348 2.0433 2.0019 2.00472.0377 2.0423 2.0267 nC 2.0155 2.0285 2.0371 1.9963 1.9990 2.0316 2.03622.0207 νd 27.4 26.3 26.7 28.4 28.2 26.9 26.8 27.0 Tg [° C.] 746 742 724728 730 731 747 744 TI(10 mm) 0.36 0.26 0.46 0.57 0.73 0.71 0.78 0.73420 nm TI(10 mm) 0.69 0.63 0.74 0.80 0.87 0.84 0.91 0.87 460 nm

TABLE 3 18 19 20 21 22 23 24 25 26 SiO₂ 6.7 5.2 5.0 5.0 5.0 5.0 5.0 5.05.5 B₂O₃ 5.9 6.2 6.0 5.9 6.0 6.5 7.0 6.5 5.5 La₂O₃ 46.5 46.6 47.0 47.147.0 47.0 43.0 47.0 47.0 Gd₂O₃ 7.7 7.7 8.0 7.9 6.0 5.0 4.0 5.0 5.0 Nb₂O₅10.5 9.7 11.0 10.7 13.0 11.0 11.0 11.0 11.5 Y₂O₃ 0.6 0.6 0.6 0.6 0.6TiO₂ 15.1 16.3 15.0 15.4 15.5 15.0 15.0 15.5 16.0 ZrO₂ 6.9 7.5 7.5 7.17.0 6.5 3.0 6.5 6.5 BaO 4.0 12.0 4.0 3.5 Sb₂O₃ HfO₂ 0.2 0.2 0.2 Σ(La₂O₃ + 79.0 80.1 80.5 80.3 82.5 79.5 72.0 80.0 81.0 Nb₂O₅ + TiO₂ +ZrO₂) Σ (La₂O₃ + 4.2 3.9 4.4 4.2 4.3 4.3 3.8 4.2 4.1 Nb₂O₅ + ZrO₂)/ TiO₂Properties Density 5.13 5.19 5.23 5.18 5.15 5.06 5.12 [g/cm³] nd 2.03612.0548 2.0616 2.0352 2.0024 2.0367 nF 2.0632 2.0830 2.0906 2.0625 2.02842.0642 nC 2.0251 2.0434 2.0499 2.0242 1.9919 2.0256 νd 27.2 26.6 26.127.0 27.5 26.8 Tg [° C.] 740 746 739 739 740 724 727 TI(10 mm) 0.83 0.800.78 0.75 0.81 0.76 0.76 420 nm TI(10 mm) 0.92 0.91 0.90 0.89 0.91 0.860.89 460 nm

Table 1 shows the example glasses 3 to 6 and 9 provided according to thepresent invention as well as the comparative examples 1, 2, 7 and 8which are not provided according to the present invention. In the caseof the comparative examples 1, 2 and 8 the sum of the portions of thecomponents La₂O₃, Nb₂O₅, TiO₂ and ZrO₂ is low. These comparativeexamples have a low refractive index. In the case of the comparativeexample 7, the weight ratio of the sum of the portions of ZrO₂, La₂O₃and Nb₂O₅ to the portion of TiO₂ is low. The comparative example 7 has arelatively low internal transmission at 420 nm and 460 nm.

Table 2 shows the example glasses 10 and 12 as well as 15 to 17 providedaccording to the present invention. The glasses 13 and 14 arecomparative examples which are not provided according to the presentinvention, with a low sum of the portions of the components La₂O₃,Nb₂O₅, TiO₂ and ZrO₂ and low refractive index. In the case of thecomparative example 11, the weight ratio of the sum of the portions ofZrO₂, La₂O₃ and Nb₂O₅ to the portion of TiO₂ is low.

Table 3 shows the example glasses 18 to 23 as well as 25 and 26 providedaccording to the present invention. The glass 24 is a comparativeexample which is not provided according to the present invention, with alow sum of the portions of the components La₂O₃, Nb₂O₅, TiO₂ and ZrO₂and low refractive index. In the case of the comparative example 24,also the weight ratio of the sum of the portions of ZrO₂, La₂O₃ andNb₂O₅ to the portion of TiO₂ is low.

The glass transition temperature T_(g) of the glasses shown in theTables 1 to 3 was in a range of 724° C. to 754° c.

Further characteristic glass properties are shown in the following Table4 exemplarily by the above-described glasses 7 to 9 and 11.

TABLE 4 7 8 9 11 CTE(20,300) [ppm/K] 8.5 8.1 8.3 8.2 T1 [° C.] 1173 11731184 1180 T4 [° C.] 954 923 960 950 T7.6 [° C.] 834 811 836 833 TK [°C.] 1140 1060 1110 1135 Viscosity at TK [dPas] ~10¹ ~10^(1.9) ~10¹⁵~10^(1.1)

Further example glass compositions (in % by weight) and properties areshown in Table 5.

TABLE 5 27 28 29 30 SiO₂ 5.5 5.4 5.4 5.4 B₂O₃ 5.5 5.3 5.4 5.1 La₂O₃ 46.846.7 46.7 46.9 Gd₂O₃ 5.0 5.1 5.1 5.0 Nb₂O₅ 11.4 11.4 11.4 11.1 TiO₂ 15.916.1 16.1 16.5 ZrO₂ 6.5 6.5 6.4 6.1 BaO 3.5 3.6 3.6 3.6 HfO₂ 0.2 Σ(La₂O₃ + 80.6 80.7 80.6 80.6 Nb₂O₅ + TiO₂ + ZrO₂) Σ (La₂O₃ + 4.1 4.0 4.03.9 Nb₂O₅ + ZrO₂)/ TiO₂ Properties Density 5.16 5.18 5.17 5.18 [g/cm³]nd 2.0491 2.0519 2.0509 2.0555 nF 2.0774 2.0804 2.0794 2.0842 nC 2.03762.0404 2.0394 2.0440 νd 26.4 26.3 26.3 26.2 Tg [° C.] 749 746 748 749TI(10 mm) 0.71 420 nm TI(10 mm) 0.87 460 nm

While this invention has been described with respect to at least oneembodiment, the present invention can be further modified within thespirit and scope of this disclosure. This application is thereforeintended to cover any variations, uses, or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains andwhich fall within the limits of the appended claims.

What is claimed is:
 1. A glass, comprising the following components in %by weight: Component Portion (% by weight) SiO₂ 2-10 B₂O₃ 2-10 La₂O₃40-55  Gd₂O₃ 4-11 Nb₂O₅ 6-14 TiO₂  8-18.5 ZrO₂  5-11;

wherein the glass has a refractive index n_(d) of at least 2.02, a sumof the portions of La₂O₃, Nb₂O₅, TiO₂ and ZrO₂ is at least 76.5% byweight, and a weight ratio of a sum of the portions of La₂O₃, Nb₂O₅ andZrO₂ to the portion of TiO₂ is at least 3.85:1.
 2. The glass of claim 1,wherein at least one of the following is satisfied: a portion of Y₂O₃ is0 to 5% by weight; a portion of BaO is 0 to 10% by weight; or a portionof HfO₂ is 0 to 1% by weight.
 3. The glass of claim 1, wherein a weightratio of a sum of the portions of La₂O₃ and Nb₂O₅ to a sum of theportions of TiO₂ and ZrO₂ is at least 2.25:1.
 4. The glass of claim 1,wherein a sum of the weight portions of Nb₂O₅ and ZrO₂ is higher thanthe weight portion of TiO₂.
 5. The glass of claim 1, wherein a weightratio of a sum of the portions of La₂O₃ and Nb₂O₅ to the portion of TiO₂is at least 3.15:1.
 6. The glass of claim 1, wherein a sum of theportions of La₂O₃, Nb₂O₅ and ZrO₂ is in a range of 55 to 75% by weight.7. The glass of claim 1, wherein a weight ratio of the portion of TiO₂to the portion of ZrO₂ is at most 3.00:1.
 8. The glass of claim 1,wherein a portion of Sb₂O₃ is at most 50 ppm.
 9. The glass of claim 1,wherein the glass has an internal transmission TI of at least 80%,measured at a wavelength of 460 nm and a sample thickness of 10 mm. 10.The glass of claim 1, wherein the portion of Gd₂O₃ is at most 9% byweight and the portion of ZrO₂ is at least 6% by weight.
 11. The glassof claim 1, wherein the portion of Gd₂O₃ is in a range of from 4.5 to 9%by weight and the portion of ZrO₂ is in a range of from 6 to 11% byweight.
 12. The glass of claim 1, wherein the portion of BaO is in arange of from 1 to 8% by weight.
 13. A glass having a refractive indexn_(d) of at least 2.02 and an internal transmission TI of at least 85%,measured at a wavelength of 460 nm and a sample thickness of 10 mm. 14.The glass of claim 13, wherein the glass comprises the followingcomponents in % by weight: Component Portion (% by weight) SiO₂ 2-10B₂O₃ 2-10 La₂O₃ 40-55  Gd₂O₃ 4-11 Nb₂O₅ 6-14 TiO₂  8-18.5 ZrO₂  5-11;

wherein a sum of the portions of La₂O₃, Nb₂O₅, TiO₂ and ZrO₂ is at least76.5% by weight and a weight ratio of a sum of the portions of La₂O₃,Nb₂O₅ and ZrO₂ to the portion of TiO₂ is at least 3.85:1.
 15. The glassof claim 13, wherein the glass comprises BaO and a portion of BaO is atleast 2% by weight.
 16. The glass of claim 13, wherein a weight ratio ofa portion of SiO₂ to a portion of B₂O₃ is at least 1:1.
 17. The glass ofclaim 13, wherein a weight ratio of a sum of the portions of La₂O₃,Nb₂O₅, TiO₂ and ZrO₂ to a sum of the portions of SiO₂ and B₂O₃ is atleast 7.15:1.
 18. The glass of claim 13, wherein the refractive indexn_(d) is at least 2.03.
 19. The glass of claim 13, wherein a weightratio of a portion of TiO₂ to a portion of BaO is in a range of from1.0:1 to 25:1.
 20. A glass article, comprising: a glass having arefractive index n_(d) of at least 2.02 and being in the form of atleast one of: a glass for eyeglasses; a stack of wafers; a wafer; awafer with a maximum diameter of 5.0 cm to 40.0 cm; a lens; a sphericallens; a prism; an asphere; a light wave guide; a fiber; or a plate;wherein the glass has an internal transmission TI of at least 85%,measured at a wavelength of 460 nm and a sample thickness of 10 mm.